Online Redo Log Switching from RMAN Backup

I was troubleshooting backup from standby databases and encountered an oddity which I wanted to verify.

Backing Up Archived Redo Logs with RMAN

Before beginning the backup, RMAN switches out of the current redo log group, and archives all online redo logs that have not yet been archived, up to and including the redo log group that was current when BACKUP command with any of the following clauses:
PLUS ARCHIVELOG
ARCHIVELOG ALL
ARCHIVELOG FROM …